Process and an apparatus for the production of a voluminous nonwoven fabric

ABSTRACT

An apparatus for producing a nonwoven fabric, including a spinneret for extruding a plurality of filaments, and a device for collecting the filaments and forming a nonwoven fabric, at least one thermal treatment device, at least one bonding device, wherein the at least one thermal treatment device includes at least one heating device configured to direct gas against said nonwoven fabric at a temperature between 80 and 190° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.16/595,990, filed on Oct. 8, 2019, the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention concerns a process and an apparatus for producinga nonwoven fabric and, in particular, voluminous nonwoven fabricsobtained by the spunbond process.

Background

As known, spunbond fabrics are obtained by extruding, drawing anddepositing a plurality of filaments of plastic material on a conveyorbelt. The filaments laid down on the belt are then constrained togetherat a plurality of points by different processes, such as for example bycalendering, applying air or water jets, or welding, etc.

A typical plant for producing spunbond filaments comprises a spinninghead fed by extruders, a drawing unit and a deposition unit fordepositing the drawn filaments on a movable support (collecting surface)where the nonwoven fabric is formed.

The nonwoven fabrics of spunbond type are used in various fields, suchas for example medical and sanitary ones, but also in the geotechnicalfield, in civil engineering, in building construction. Depending on theapplication, the nonwoven fabric must have different mechanical featuresrelating to finishing, resistance to particular agents, etc., so as tomeet the different requirements of the areas of use.

Nonwoven fabrics are known in the art which are made from filamentsformed by two or more components, so as to be able to exploit differentcharacteristics of the employed materials.

It is known, for example, to arrange two polymer materials inside-by-side arrangement. In the side-by-side design, two polymermaterials are coextruded so as to form a multicomponent filament inwhich the two materials form two sub-filaments next to each other.Typically, the multicomponent filament has circular section and the twosub-filaments have semicircular sections. In other words, the section ofthe contact surface between the two filaments substantially coincideswith the diameter of the section of the multicomponent filament. It isalso known to vary the ratio between the two components. In this case,the contact surface between the two sub-filaments coincides with a chordof the circular section of the multicomponent filament. Similarside-by-side filaments are described, for example, in U.S. Pat. No.5,382,400 and US 2013/0029555.

It is further known to select the materials of the two sub-filamentswith different characteristics so as to cause the multicomponentfilament to crimp. Such a shape is used for providing the final nonwovenfabric with increased softness and volume, among other things.

For example, the two sub-filaments can be made up of materials havingdifferent features, whereby the multicomponent filament is initiallyextruded and drawn, thus forming a not-crimped continuous filament. Whenthe multicomponent filament is deposited on the collector, the twosub-filaments behave differently, thus crimping the multicomponentfilament.

Similarly, the two sub-filaments may be made up of materials havingdifferent coefficients of thermal expansion. If the multicomponentfilament is subjected to thermal treatment, the two sub-filamentsexpand/shrink in a different way with respect to one another thuscrimping the multicomponent filament.

Additionally, it is known to manufacture the two sub-filaments ofmaterials different from one another, resulting in uneven stressesbetween the two sub-filaments during the extrusion and drawing stepsthat cause the multicomponent filament to be crimped.

Processes are known, wherein the crimp develops before depositing thefibers on the collecting belt, as described in US2009/0152757 andUS2008/0210363 in the name of Reifenhauser. In fact, such documentsteach to exploit a diffuser for activating the natural fiber crimp, thediffuser being arranged downstream of the means for drawing thefilaments that are therefore deposited already crimped on the conveyorbelt, to be then further crimped by appropriate treatments (therebymaking a so-called “primary crimping”, before depositing, and a“secondary crimping”, after depositing). However, the treatment offibers already crimped is complex and does not lead to satisfactoryresults. Moreover, processes are known for crimping even materialshaving low reciprocal adhesion properties. For example, U.S. Pat. No.3,458,390 teaches to make side-by-side multicomponent filaments in whichthe contact surface between the two filaments provides a shape coupling(by means of “undercuts”), so as to mechanically constrain or entanglethe sub-filaments to one another. Therefore, the two sub-filaments arebonded by such mechanical constraint and do not split during therequired treatments (for example thermal treatments). It is difficult toobtain such a shape. Moreover, excessive stress may cause theundesirable splitting of the multicomponent filament. Finally, it is notknown how to make a nonwoven fabric by such multicomponent filament.

Therefore, it is an object of the present invention to make a spunbondnonwoven fabric having high crimping level and thus high volume level.It is a further object of the present invention a spunbond methodallowing this nonwoven fabric to be simply and economically produced.

These and other objects are achieved by the present invention by meansof a process and an apparatus according to independent attached claims.Preferred aspects are set forth in dependent claims.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a process for producinga nonwoven fabric comprises the steps of:

-   -   (a) extruding a plurality of filaments from a spinneret;    -   (b) collecting the filaments in a substantially not-crimped        condition to make a nonwoven fabric;    -   (c) carrying out a thermal treatment of the nonwoven fabric to        increase the volume of the nonwoven fabric, comprising at least        the step of heating said nonwoven fabric;    -   (d) bonding the nonwoven fabric.

In particular, during step (c), at least part of the filaments of thenonwoven fabric develops a “crimp” so that the volume of the nonwovenfabric is increased. In other words, the invention provides fordepositing the filaments in a not-crimped condition to form asubstantially flat nonwoven fabric (i.e. mainly bidimensional) andtreating them to increase the nonwoven fabric volume, that is for makinga voluminous nonwoven fabric.

Typically, at least steps (a)-(c) are carried out sequentially, whereasthe steps (c) and (d) can be carried out sequentially orcontemporaneously by the same device. Moreover, the steps (c) and (d)can be carried out also in a different equipment or anyway at a timevery apart after step (b). In other words, the use of an equipment tocarry out steps (a) and (b) can be provided in such a way to obtain asemifinished product usable in the following, for example in a differentequipment, to carry out steps (c) and (d).

It has to be noted that the difference between the crimped condition andthe not-crimped condition of a filament is known to the field technicianand, in particular, the filaments in the not-crimped condition aresubstantially free of loops. On the contrary, crimped filaments have aplurality of loops and a wavy and irregular pattern, whereby the lengthof a crimped filament is appreciably lower than the length of the samefilament in not-crimped condition.

The filaments of the present invention are deposited in a not-crimpedway. Therefore the not-crimped filaments, when deposited, have a “crimppercentage” typically higher than 50%, and preferably higher than 70%.The “crimp percentage”, known in the art, can be for example measured bymaking two signs spaced from one another on a filament to be tested andmeasuring the distance between the two signs along a straight line. Thesame filament is then extended (i.e. it becomes straight) and thedistance between the two signs is measured again. The percentage ratiobetween the first value and the second value of the distance, as known,is the value of the “crimp percentage”.

Another definition of crimped filaments is provided, for example, in theReifenhauser's Application US20090152757, according to which thefilaments are considered “crimped” if they have a curvature radius lowerthan 5 mm in the relaxed condition.

According to a possible aspect, an entangling step is carried out, atleast partially, to entangle filaments laid down before making a thermaltreatment. Such initial entangling can be carried out, for example, by acouple of rollers between which the nonwoven fabric is passed, thenproviding a first packing and pre-setting (i.e. pre-bonding) of thenonwoven fabric. A constraint or entangling stronger than what can beobtained with the mentioned couple of rollers between the filaments canbe made by an appropriate constraining or entangling device; forexample, suitable devices are selected from a needle loom and anultrasound device.

Preferably, in case of presence of the constraining or entanglingdevice, a first setting of the nonwoven fabric happens, such that thecrimping of the filaments is allowed during the following thermaltreatment and another setting of the nonwoven fabric happens after thethermal treatment (i.e. after the filaments have been crimped and thevolume of the nonwoven fabric has increased), so that to set the finalshape of the nonwoven fabric.

An aspect of the present invention is therefore a process for producinga voluminous nonwoven fabric, comprising the steps of extruding aplurality of bicomponent filaments from a spinneret; collecting saiddrawn filaments on a collecting surface to form a nonwoven fabric;subjecting said nonwoven fabric to a step providing an at least partialentanglement of the filaments; increasing the volume of said at leastpartially entangled nonwoven fabric by means of at least one thermaltreatment and bonding (i.e. setting) the bulked (“voluminized”—increasedin volume) nonwoven fabric.

The heating step is carried out at a temperature selected as a functionof the type of polymer used in the filament production; suitabletemperatures are generally between and 190° C., as a function of themelting points of polymers used in producing the nonwoven fabric.

According to a particular aspect of the present invention, the thermalbulking treatment of the nonwoven fabric provides for a pre-heating stepof the nonwoven fabric preceding the heating step, carried out at atemperature lower than the heating step. Typically, the temperaturedifference between the pre-heating step and the heating step is higherthan 5 degrees, preferably is higher than 10 degrees Celsius.

According to a preferred aspect, the heating step (c) is carried out bya drum oven, wherein the nonwoven fabric is fed to a rotary drum and hotgas is directed radially with respect to such drum, typically in adirection centripetal with respect to the drum, so that to cross thenonwoven fabric being on the drum and the drum itself.

The heating step aids the crimp development and also the setting of thestructure of the nonwoven fabric.

This setting can be completed in the heating step or can be carried outinside an apposite bonding device to bond the nonwoven fabric, typicallyby at least one calender. In possible implementations, both mentionedsetting methods are carried out.

The pre-heating step promotes the volume increase of the nonwoven fabricvolume via the crimp development, in particular in case wherein thetreatment time inside the drum oven (or similar heating means) is notsufficient to guarantee an appropriate crimping.

In an embodiment, the pre-heating step is carried out by passaging thenonwoven fabric inside a device in which heated gas, preferably air, isdirected against the nonwoven fabric along an angled direction,preferably perpendicular to the plane along which the nonwoven fabricmoves forward. According to a possible aspect, the flow direction of thehot air is directed contrary to the gravity, i.e. from bottom to topthrough the movable belt supporting the nonwoven fabric, in order to aidthe bulking (“voluminization”—increase of volume) of the nonwovenfabric. Alternative embodiments in which the gas flow is orientedsubstantially coincident with the gravity are not excluded, or anywayfrom top to bottom. In other words, the heating is preferably carriedout by a drum oven, whereas the pre-heating is preferably carried out bya different device with straight forward movement of the nonwovenfabric.

On the contrary, in possible embodiments only the drum oven is used. Inthis case the filament crimping of the nonwoven fabric and theconsequent bulking of the nonwoven fabric happen substantially insidethe oven itself. In an embodiment, the oven comprises two rotary drums,in another embodiment there are two drum ovens in series.

In a preferred embodiment, therefore the process of the inventionprovides the following steps in succession:

-   -   (a) extruding a plurality of filaments from a spinneret, wherein        the filaments preferably comprise two sub-filaments adhered to        each other and arranged in accordance with a side-by-side        configuration, wherein the contact surface between the two        sub-filaments, in the cross-section of the filament, is        substantially wave-shaped and/or the melting temperature        difference of the materials of the two sub-filaments is at least        10° C.; (    -   b) collecting the filaments in a substantially not-crimped        condition to form a nonwoven fabric;    -   (b′) carrying out a constraining or entangling step of the        deposited filaments,    -   (c) thermal treating the nonwoven fabric to increase the volume        of the nonwoven fabric, comprising at least one step (c2) of        heating the nonwoven fabric, and preferably comprising a        pre-heating step (c1) before the mentioned step (c2) of heating        the nonwoven fabric;    -   (d) optionally, bonding the nonwoven fabric.

As previously described, the constraining or entangling step (b′) can becarried out by a couple of rollers between which the nonwoven fabric ispassed and/or by an entangling device, preferably selected between aneedle loom and an ultrasound device. Among the possible listedsolutions the ultrasound device is the preferred one, since it allowsthe filaments to be constrained more precisely and allows to defineentangled points (or zones) on the nonwoven fabric among the filamentsmore simply. In particular, thanks to an ultrasound device, the distancebetween the various entangled points among the filaments of the nonwovenfabric can be adjusted. During the crimping step, as a matter of fact,the volume (and in particular the thickness) of the nonwoven fabricincreases at the portions not-constrained, i.e. not-entangled, to oneanother, whereas the thickness of the nonwoven fabric remainssubstantially unchanged at the entangled points or zones (therebyforming a “quilted” effect).

In case of presence of both the elements (couple of rollers andconstraining device), the constraining device is arranged downstream ofthe couple of rollers.

In particular, an aspect of the invention provides for carrying out thenot-crimped deposit of bicomponent filaments having side-by-sideconfiguration as described above, carrying out a first constraintbetween the same, preferably by using at least one constraining devicesuch as a needle loom or an ultrasound machine, thermically treating thenonwoven fabric (by heating it) so that the filaments are crimped sothat the volume, in particular the thickness, of the nonwoven fabricitself is increased. The thermal treatment is preferably carried out intwo steps, i.e. the pre-heating and the heating.

The presence of an at least partially constraining or entangling step(in particular by needlefelting or ultrasound treatment) allows somestructural stability to be conferred to the nonwoven fabric. Thanks tothis, the non-woven fabric subjected to “entangling” but not yet bulkedby heating, can be for example wound on the spool and can preserve thespool shape (or other shape adapted to be transported, stored and thelike) until the use time. Therefore, the nonwoven fabric can betransported, stocked and usually maintained in a not-voluminous shape(i.e. having a flat shape) and then be put again in a treating plant tobe bulked and undergo possible finishing operations (such as the cuttingof the nonwoven fabric for producing an item with such a nonwovenfabric).

More in detail, during the thermal treatment, the filaments of thenonwoven fabric crimp and the nonwoven fabric increases its volume, inparticular it increases its own thickness. Such thickness increase canbe limited (or substantially absent) at the points treated by theconstraining or entangling device. In other words, the constrainingdevice (needle loom or ultrasound machine) constrains the filaments ofthe nonwoven fabric one to another in some points, and the volumeincrease of the nonwoven fabric during the thermal treatment occursaround these points; therefore the bulked nonwoven fabric will have anappearance reflecting the presence of more bulgy or less bulgy zones,where the less bulgy zones are those partially constrained. Therefore,by adequately selecting where the constraining device has to operate,some structural stability can be imposed to the nonwoven fabric, so thatthe storage and the transportation are facilitated.

In addition to a process for making a nonwoven fabric, an aspect of thepresent invention relates to an apparatus for making a nonwoven fabric.

According to an aspect, an apparatus for producing a nonwoven fabriccomprises a spinneret for extruding a plurality of filaments, means forcollecting the filaments and forming a nonwoven fabric, at least onethermal treatment device for thermally treating the nonwoven fabric, atleast one bonding device to bond the nonwoven fabric; the at least onethermal treatment device comprises at least one heating deviceconfigured to direct gas, preferably air, on the nonwoven fabric at atemperature preferably between 80 and 190° C.

According to a possible aspect, the heating device comprises a drum ovenprovided with a rotary drum for receiving the nonwoven fabric, and meansfor generating a heated gas flow, preferably air, towards the sidesurface of the rotary drum, preferably in a substantially radialdirection with respect to the rotary drum.

According to a possible aspect, the apparatus comprises a pre-heatingdevice configured to direct the gas, preferably air, against thenonwoven fabric at a temperature between 70 and 185° C.

According to a possible aspect, the pre-heating device comprises atleast one first surface arranged substantially parallel to the forwarddirection of the nonwoven fabric and means for generating a gas flow ina direction substantially incident to the forward direction of thenonwoven fabric, preferably substantially perpendicular to the mentionedforward direction (D) of the nonwoven fabric.

According to a possible aspect, said pre-heating device comprises asecond surface arranged substantially parallel to the first surface, andthe first and second surfaces are arranged so that, in use, the nonwovenfabric moves forward along said forward direction between the first andsecond surfaces. Preferably, the distance between the mentioned firstand second surfaces is variable, to have the possibility of adapting tothe bulking of the nonwoven fabric.

According to a possible aspect, a device for cooling the nonwoven fabricis arranged downstream of the pre-heating device. Such a cooling deviceis arranged so that a gas flow is directed along a direction incident,preferably substantially perpendicular, to the forward direction of thenonwoven fabric.

According to a possible aspect, the apparatus spinneret is arranged sothat a bicomponent filament is extruded, the latter comprising twoside-by-side arranged sub-filaments in which the contact surface betweenthe two sub-filaments has a substantially wave-shaped cross section.

According to a possible aspect, a device for constraining the filamentsone to another, preferably selected between a needle loom and anultrasound machine, is arranged upstream of the heating device and alsoof the pre-heating device, if present.

According to a possible aspect, the constraining device and at least onebetween said pre-heating and heating devices can be arranged in acondition of disengagement from the nonwoven fabric so that a treatmenton the latter is not carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary and not limiting embodiments of the present invention are nowillustrated with reference to attached figures, in which:

FIG. 1 is a schematic view of an apparatus for producing a nonwovenfabric according to a first embodiment;

FIG. 2 is a schematic view of an embodiment alternative to that of FIG.1 ;

FIG. 3 is a schematic view of the apparatus of FIG. 2 , in which theconstraining and pre-heating devices are arranged in a configuration ofdisengagement from the nonwoven fabric carried by the collecting means;

FIGS. 4 a and 4 b are sectional views of possible filaments usable toform a nonwoven fabric with an apparatus according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

An apparatus 10 for producing a nonwoven fabric 150 comprises, as known,a device 1 for extruding continuous filaments 100 and for depositingthem on collecting means 2. For this purpose, various devices 1 known inthe art can be used. For example, it is possible to use the devicesdescribed in the Applications WO2008/072278 and WO2008/075176.

In general, such devices have a spinneret 1 a for extruding a pluralityof filaments 100, typically followed by a drawing unit 1 b. Generally, acooling zone, not shown and known in the art per se, is arrangedupstream of the drawing unit to direct air flows to the filaments 100after the extrusion from the spinneret 1 a, so that they are cooledappropriately. A possible cooling chamber usable in the presentinvention is for example described in the Patent EP1939334; such Patentdescribes also a filament extruding and collecting device adapted to beused in the present invention. Below the device 1 there are thecollecting means 2, typically in the form of conveyor belt or the like.The collecting means 2 are typically pierced or anyway gas-permeable.Appropriate means, not shown in detail and typically in the form ofaspirator or similar element, can be provided below the collecting means2 so that a depression is created at the zone in which the filaments 100are deposited on the same collecting means 2.

A couple of rollers 9 can be arranged at the collecting means 2, so thata first setting (constraining) and sizing of the nonwoven fabric can becarried out. The rollers 9 can further prevent (or at least limit) theair inflow from the outside of the device 1 for the extrusion anddeposit of the filaments towards the inside of the device itself. Inparticular, the air inflow is prevented or limited from the outside ofthe device 1 to the collecting device 2, which has a depression zoneadapted to promote the filament deposit. In other words, the rollers 9can be placed in contact with the nonwoven fabric thus providing someairtightness, so that the air inflow from the outer environment to theinside of the device 1 is limited. The depression inside the device 1,provided at the collecting means 2, anyway draws mainly the air alreadypresent inside the device 1 itself.

The continuous filaments 100 can be differently shaped. The filamentscan be mono-component or multi-component. In a preferred implementationthe continuous filaments 100 are bi-component, i.e. they have twosub-filaments 100 a, 100 b coupled one another. The bicomponent filament100 can have different configurations, for example core-sheath or, morepreferably, side-by-side.

According to an aspect of the present invention shown in the figures,the filaments 100 comprise two sub-filaments 100 a, 100 b made bycoextruding two typically polymeric materials. The sub-filaments 100 a,100 b are arranged in side-by-side configuration. A particularconfiguration of the filaments 100 is described in detail in thecopending Application EP16198713.

In particular, the materials for the two sub-filaments 100 a, 100 b arepreferably selected among PP, coPP, PE, CoPE, PET, CoPET, PA, PLA.Preferred combinations are: PP/PE, PP/CoPP, PP/PP, PET/PP, PET/CoPET,PA/PP, PLA/PP, PLA/PE. According to a preferred embodiment, thematerials of the sub-filaments 100 a, 100 b are selected so that thecrimping of the latter is allowed during a thermal treatment. This ispreferably obtained by at least one of the following features: thedifference of the melting temperature of the sub-filaments 100 a and themelting temperature of the sub-filaments 100 b is at least 10° C., andpreferably at least 20° C.; the viscosity of the two materials of thesub-filaments 100 a, 100 b is different, preferably the difference beinghigher than 20% when measured by the same method and in the sameconditions. For example, the two materials can be tested with the sameviscometer (for example a rotational or capillary one) or, more ingeneral, the viscosity can be determined by a common method defined in arecognized standard (for example, ASTM D3835). In other words, for thesub-filaments, polymers can be selected having different melting pointand similar viscosity, or polymers with equal or similar melting pointbut different viscosities, or else two polymers having different meltingpoints and viscosities. As mentioned, the preferred configuration of thetwo sub-filaments 100 a, 100 b is the side-by-side one providing the twosub-filaments being next to each other so that, in section, the twosub-filaments 100 a, 100 b are divided by a line representing thecontact surface 105. According to a preferred aspect of the invention,the contact surface 105 is waveform, i.e. a configuration containing atleast one inflection point. In other words, the shape of thecross-section of the contact surface shows at least one peak 101, 102alternating with at least one trough 103. As known, “peaks” and“troughs” are the crests 101, 102, 103 formed by the wave, i.e. themaxima and the minima. The peaks 101, 102 are directed in the oppositedirection with respect to the troughs 103. It should be noted that,typically, the difference between troughs 103 and peaks 101, 102 isgiven only by the orientation chosen for the section of the filament.

According to an aspect of the present invention, the section of thecontact surface 105 forms a wave with at least three crests 101, 102,103; in particular, in preferred embodiments there are exactly threecrests 101, 102, 103. For convenience sake, two peaks and one troughwill be referred to.

According to an aspect, the period T of the wave is between 40% and 100%of the length of the diameter of the multicomponent filament 100. Itshould be noted that, for convenience sake, reference will be made tothe “diameter” of the multicomponent filament 100. However, thefollowing description can be applied also to the case of a not-circularfilament section. In this case, the “diameter” should be considered asthe greatest dimension of the section. If the troughs 103 and the peaks101, 102 have the same length, then as a result the length of eachtrough and peak is preferably between 20% and 50% of the diameter (i.e.between ⅕ and ½ of the diameter).

As known, the period “T” of the wave is the sum of the lengths of atough and a peak. The period T may also be measured as the distancebetween two subsequent peaks (or toughs).

More in general, according to an aspect of the present invention, thecontact surface 105 changes at least once its own curvature, i.e. has atleast one inflection point. Typically, the section of the contactsurface covers at least one period of the waveform. More preferably, thecontact surface has at least two peaks and one trough, thus covering atleast 1.5 periods of the waveform. In a possible embodiment, thewaveform meets the edge of the filament section at the middle pointbetween trough and peak, i.e. far from the trough and/or peak adjacentto the edge.

In a preferred embodiment shown in FIG. 4 a , the waveform issubstantially sinusoidal. It should be noted that, due to the small sizeof the filament section, the waveform will actually approximate to asinusoid. In particular, in FIG. 4 a the ideal shape of the section ofthe filament 100 is shown, having length of 1.5 periods and strictlysinusoidal form. In FIG. 4 b a possible real pattern of the section ofthe contact surface 105 is shown, the wavelength of the contact surfacebeing little greater than the T period, the peaks being cut at thesection edge and the waveform approximating a sinusoid without strictlycomplying with geometrical parameters thereof.

The apparatus 10 further has various devices 3 a, 3 b, 4 a, 4 b, 5, 6 a,6 b, 7, 8 for treating the nonwoven fabric obtained from the deposit ofthe filaments 100.

In particular, the apparatus 10 can have a device 3 a, 3 b forconstraining at least part of the filaments 100 one to another, i.e. forcarrying out a so-called “entangling” between them. In the art differenttypologies of constraining or “entangling” devices 3 are known, and inparticular mechanical, hydraulic (hydroentangler) or thermal devices.Preferably, according to an aspect of the present invention, theconstraining device is selected between a needle loom 3 a and anultrasound machine 3 b. The device 3 a, 3 b is particularly useful incase wherein specific constraints among the filaments are required, orthe afore described step c) and d) must be carried out in a differentequipment or anyway in a subsequent time.

The apparatus 10 comprises at least one heating device 4 b of thenonwoven fabric 150 and, preferably, also a pre-heating device 4 aplaced upstream of the heating device 4 a. In case of presence of theconstraining device 3 a, 3 b, the heating and pre-heating devices 4 a, 4b are arranged downstream of the former. In an embodiment, thepre-heating device 4 a is configured to heat the gas to be directed onthe nonwoven device at a temperature between 70 and 180° C., whereas theheating device is configured to heat the gas to be directed against thenonwoven fabric at a temperature between 90 and 190° C.

According to a particular embodiment, the pre-heating device 4 a has atleast one first supporting surface 41 a for the nonwoven fabric 150, onwhich the nonwoven fabric 150 is arranged. The surface 41 a is typicallymovable so that to match with the movement of the nonwoven fabric 150.The surface 41 a is further typically gas-permeable, so that the passageof a flow of gas G1 is facilitated, as better described in thefollowing, through the nonwoven fabric 150.

The embodiment shown in the figures further has a second surface 42 aarranged substantially parallel to the forward direction D of thenonwoven fabric 150. The two surfaces 41 a, 42 a are arranged so thatthe supporting surface of the nonwoven fabric 150 (i.e. the firstsurface 41 a in the shown embodiment) is arranged below the nonwovenfabric 150, and the other surface (i.e. the second surface 42 a in theshown embodiment) is arranged above the nonwoven fabric 150. The secondsurface 42 a is preferably movable, too, so that to match the movementof the nonwoven fabric 150 along the travel thereof.

Even if the preferred embodiment provides two surfaces 41 a, 42 a incontact with the nonwoven fabric 150, possible embodiments are anywaypossible in which only one surface contacts the latter. In particular,embodiments are possible in which the nonwoven fabric 150 contacts onlyone surface arranged below such a fabric, i.e. embodiments not having,with reference to that shown in the figures, the second surface 42 a.

The pre-heating device 4 a is further provided with means 45 a forsupplying or generating a flow of gas G1, typically air, to the nonwovenfabric. The means 45 a are particularly configured to heat the flow ofgas G1 to a temperature between 70 and 180° C. Such means are known inthe art and herein not discussed in detail. Typically the means 45 a arearranged so that to supply or generate a flow of gas G1 incident to thenonwoven fabric 150, and preferably a flow of gas G1 substantiallyperpendicular to the nonwoven fabric 150. The flow of gas G1 istypically oriented so that to cross the nonwoven fabric along adirection opposite to the gravity, i.e. from bottom to top. The nonwovenfabric is then urged by the flow of gas G1 upwards, so that its volumeincrease is favored.

According to a particular aspect, the pre-heating device 4 a has aportion 43 a arranged, in use, below the nonwoven fabric 150 and anotherportion 44 a that, in use, is arranged above the nonwoven fabric 150.Preferably, at least one of the two portions 43 a, 44 a is furthermovable with respect to the nonwoven fabric 150 along a directionperpendicular to the forward direction D of the nonwoven fabric itself.In other words, the distance between the two portions 43 a, 44 a, and inparticular between the surfaces 41 a, 42 a, is adjustable. In the shownembodiment, only the portion 44 a being, in use, arranged above thenonwoven fabric 150, is movable perpendicularly to the nonwoven fabric150.

It should be noted that the means 45 a for creating a gas flow areschematically shown coupled with the portion 43 a arranged below thenonwoven fabric 150. However, the arrangement of such means (for examplesuctioning means) in the portion 44 a above the nonwoven fabric 150 isnot excluded, or both the portions 43 a, 44 a may be provided with means45 a for generating or supplying a flow of gas G1. Moreover, in notshown variations of the present invention, the pre-heating device 4 amay be completely arranged above or below the nonwoven fabric 150, inparticular in case wherein such device 4 a is provided with a singlesurface 41 a through which the flow of gas G1 passes.

Moreover, in further alternative embodiments, the flow of gas G1 canface downwards and in particular substantially in parallel and with thesame way of the gravity, i.e. being oriented in the same way of thegravity.

As mentioned, the flow of gas G1 is preferably an air flow.

According to a possible aspect of the present invention, the pre-heatingdevice 4 a is coupled to a cooling device 5. The cooling device 5 can beconfigured in a similar manner with respect to the pre-heating device 4a and use a gas flow. The cooling device 5 can further have at least onesurface 51, 52 and preferably two surfaces 51, 52 arranged in parallelto the forward direction D of the nonwoven fabric, the two surfacesbeing preferably movable. The cooling device 5 is further provided withmeans 55 for generating a flow of gas G3, preferably air, at ambienttemperature or anyway lower than the temperature of the flow of gas G1.Preferably the temperature of the flow of gas G3 is between 30 and 140°C.

The flow of gas G3 can have direction incident to the nonwoven fabric150 and, preferably, substantially perpendicular to the nonwoven fabric150. The flow of gas G3 is also oriented to cross the nonwoven fabricalong a direction opposite to the gravity, that is from bottom to top,even if the possibility of directing the flow of gas G3 from top tobottom is not excluded.

As mentioned, the apparatus 100 is provided with a heating device 4 bprovided with means 42 b for generating a flow of gas G2, preferablyair, directed against the nonwoven fabric 150. In an implementation,such flow of gas G2 has temperature between 80 and 190° C.

Preferably, the heating device 4 b comprises at least one drum oven. Inparticular, the heating device 4 b is preferably provided with a rotarydrum 41 b adapted to receive and carry the nonwoven fabric 150 into theoven itself

The heating device 4 b further has means 42 b for generating a flow ofgas G2 heated to a temperature between 80 and 190° C. The gas flow ispreferably directed radially with respect to the rotary drum 41 b.Typically, such flow of gas G2 is directed towards the centre of therotary drum 41 b, so that to cross the nonwoven fabric and the drum.

Such means 42 b, known in the art, can be arranged for example insidethe drum 41 b so that to suck a properly heated flow of gas G2, oroutside thereof, such that a flow of gas G2 is forced against the drum41 b.

Preferably, at the inlet of the heating device 4 b there is a roller 6 aadapted to direct the nonwoven fabric 150 into the same device.According to a possible aspect, the roller 6 a is provided with an airsuctioning system, such that the nonwoven fabric 150 is attracted andcooled at the same time. The roller 6 a generally has size smaller thanthe rotary drum 41 b.

Analogously, a roller 6 b is preferably arranged at the outlet of thenonwoven fabric from the heating device 41 b. Such a roller can have anair suctioning system, too, such that the nonwoven fabric 150 isattracted and cooled at the same time.

Generally, when there are both the pre-heating and heating devices 4 a,4 b, preferably first cooling means 5, 6 a are arranged between them. Inthe shown embodiment, such first cooling means 5, 6 a comprise the aforedescribed cooling device 5 and roller 6 a. Anyway, embodiments in whichthere is only one of such first cooling means are possible, and alsoembodiments in which cooling means different from the cooling device 5and the roller 6 a are arranged between the two heating devices 4 a, 4b.

Downstream of the heating device(s) 4 a, 4 b, a bonding device 7 isarranged. Various bonding devices are known in the art and can be usedin the present invention such that the nonwoven fabric layer is set.

According to a preferred aspect, the bonding device 7 comprises acalender. Such calender can have reliefs so that the nonwoven fabric isembossed, such an embossing being adapted to provide the nonwoven fabricwith various cohesion points without impairing the crimping effectpreviously obtained.

Preferably, there are second cooling means 6 b, 8 between the heatingdevice 4 a, 4 b and the bonding device 7. Such second cooling means cancomprise the previously described roller 6 b and/or a cooled conveyorbelt 8. The conveyor belt 8 can be cooled thanks to means known in theart and herein not described in detail, for example air suctioning meanscan be used.

In addition or substitution of the roller 6 b and/or the belt 8,different means for cooling the nonwoven fabric 150, known in the art,can be used.

According to a possible embodiment shown in FIG. 3 , the constrainingdevice 3 a, 3 b and the pre-heating and heating device(s) 4 a, 4 b canbe arranged in a condition of disengagement from the nonwoven fabric150. This allows the apparatus 100 to operate like a conventionalapparatus for producing a spunbond nonwoven fabric according to theknown art.

Typically, in such operative condition, the arrangement of thecollecting means 2 is modified. In particular, in the embodiment of FIG.3 , the collecting means 2 are arranged on the apparatus 1 so that thenonwoven fabric 150 is moved at least up to the heating means 4 b (thedrum oven) and possibly up to the bonding means 7. In such conditions,in fact the filaments can be treated directly by the bonding device orcan be treated also by the drum furnace, for example to further pre-setthe nonwoven fabric or to dry the nonwoven fabric in case the latter hasbeen treated with any agent; in such condition, the standard nonwovenfabric does not crimp inside the drum oven. The filaments 100, in use,are extruded from the spinneret la and deposited on the collecting means2, typically after been passed through a drawing unit 1 b.

Differently from known solutions, as those described in US2009152757 andUS2008210363, the filaments 100 laid down on the collecting means 2 aredeposited in a not-crimped condition, i.e. they are substantially freeof loops when deposited on the collecting means 2. Therefore, thenonwoven fabric 150 deposited on the collecting means 2 has thicknesstypically comparable to that of the standard spunbond nonwoven fabricsmade with mono- or bicomponent filaments.

As afore described, the filaments 100 are bicomponent filaments, havingtwo sub-filaments 100 a, 100 b arranged in a side by side configuration,the contact surface being preferably wave shaped when seen in the crosssection.

Referring to FIG. 4 a , a possible method for obtaining a wave shape isnow described in detail. In particular, the first sub-filament 100 a isextruded under a constant pressure P1. The extrusion pressure, i.e. thespinning pressure, of the second sub-filament varies, for example insinusoidal way, between two values P0 and P2. P0 is smaller than P1,whereas P2 is greater than P1. The second filament 100 b forms aprotrusion within the first sub-filament P1 where the secondsub-filament is extruded under pressure P2 (i.e. under a pressure higherthan the pressure of the first sub-filament 100 a). Conversely, thefirst sub-filament forms a protrusion within the second sub-filament 100b where the second sub-filament 100 b is extruded under a pressure P0(i.e. a pressure lower than the pressure of the first filament).

For the sake of simplicity, an embodiment in which only the pressure ofone of the two sub-filaments 100 b is varied, has been described.However, in order to obtain a desired shape (e.g. wavy), the extrusionpressure can be varied at different areas of both the sub-filaments 100a, 100 b. Generally, the second sub-filament forms a protrusion withinthe first sub-filament where the pressure of the second sub-filament isgreater than the pressure of the first sub-filament, and vice versa.

The filaments 100, once laid down on the collecting means, form anonwoven fabric 150.

According to a possible embodiment, the nonwoven fabric 150 can betreated by a couple of rollers 9. In particular, the filaments 100 aredeposited on the belt in a random (loose) way, thus resulting in anirregular arrangement of the filament, showing however a substantiallyuniform density. At this point, the nonwoven fabric 150 has notundergone yet a constraining process of the filaments, whereby it ispreferable to carry out a treatment compacting the filaments enough tobe able to be subjected to subsequent treatments thereof.

For this purpose, the filament layer is passed through two rollers 9 sothat a first constraint (or pre-set) of the filaments of the nonwovenfabric is effected. The upper cylinder can be provided with means forheating it to a temperature between 50° C. and 140° C., generally around90° C., and anyway temperatures selected depending on the nature of theemployed polymers and to provide a first filament cohesion.

As previously mentioned, the coupling between the rollers 9 and thenonwoven fabric preferably avoids, or at least limits, the ambient airinflow into the device 1, at the collecting means 2.

A constraining step 3 a, 3 b can be carried out between the deposit ofthe nonwoven fabric 150 and the heating inside the device 4 b, by anadapted device known in the art. Preferred devices are selected betweena needle loom 3 a and an ultrasound machine or device 3 b. Among thesesolutions, the preferred is an ultrasound machine 3 b, i.e. a device forcarrying out the so-called “ultrasonic bonding”. Thanks to this machine,the filaments can be constrained to one another in different points orzones, in a particularly precise way. The thickness increase of thenonwoven fabric 150, as described above, occurs at the zones which havenot been joined by the constraining or bonding device 3 a, 3 b. Thethickness increase is therefore “guided”, i.e. due to the precisedefinition of points or zones in which the filaments of the nonwovenfabric are constrained, the final shape of the nonwoven fabric followingthe filament crimping can be pre-determined, in certain limits. Ingeneral, a pattern of the points or zones in which the filaments areconstrained to one another is preferably defined on the surface of thenonwoven fabric, and the ultrasound device 3 b is particularly effectivefor this purpose. As described, by selecting such a patternconveniently, the final shape of the nonwoven fabric can be determinedby selecting which zones of the nonwoven fabric will increase theirthickness appreciably during the following crimping of the filaments andwhich zones will keep, on the contrary, substantially the samethickness. An accurate and precise definition of the zones or points inwhich the filaments are constrained further allows the nonwoven fabric150 not to be excessively stiffened, even after the constraining step.According to an aspect of the invention, the constraining device 3 a, 3b can be arranged downstream of the rollers 9, or in substitutionthereof.

Then, the nonwoven fabric is thermically treated by a heating device 4 band, more preferably, by a pre-heating device 4 a and a heating device 4b.

Preferably, the thickness of the nonwoven fabric after the thermaltreatment inside the device 4 b (or the devices 4 a and 4 b) is at least1.5 times the thickness of the nonwoven fabric 150 having not-crimpedfilaments before the heating step.

In particular, inside the pre-heating device 4 a, the nonwoven fabric150 undergoes a flow of gas G1 at a temperature between 70 and 180° C.Such temperature proves to be adapted to allow a first “activation” ofthe nonwoven fabric 150, i.e. to allow the crimping in the filaments 100of the nonwoven fabric 150, so that their volume increases.

As mentioned, the flow of gas G1 is preferably directed from bottom totop, so that the thickness increase of the nonwoven fabric 150 isfavored.

Preferably, in at least part of this step, the nonwoven fabric 150 is incontact with the pre-heating device 4 a, both above and below, thanks tothe first surface 41 a and the second surface 42 a, respectively; asdescribed before, such surfaces are preferably movable so that thenonwoven fabric 150 is accompanied along its own travel inside thedevice itself.

Subsequently, the nonwoven fabric is sent to the heating device 4 b sothat the crimping, and therefore the expansion of the former, arecompleted and, preferably, in order to carry out a thermal pre-setting(thermobonding) of the nonwoven fabric 150.

Before the nonwoven fabric enters the heating device 4 b, it can becooled by appropriate cooling means 5, 6 a. Such means can comprise, forexample, a cooling device 5 adapted to direct a flow of gas G3 againstthe nonwoven fabric 150 and/or a suctioning roller 6 a. In fact, in casethe filaments of the nonwoven fabric are transported in a sufficientlynot-solidified condition due to a high temperature, the filaments couldattach to the device moving the nonwoven fabric.

Inside the heating device 4 b, a flow of gas G2 at a temperature between80 and 190° C. is directed against the nonwoven fabric 150. In general,when there are both the pre-heating device 4 a and the heating device 4b, the operating temperature of the two devices (in particular thetemperature between the flows of gases G1 and G2) can be different of atleast 5° C. and preferably at least 10° C., and in particular thetemperature in the heating device 4 b is higher.

The nonwoven fabric 150 exiting from the heating device(s) 4 a, 4 b issent to a bonding device 7, for example a calender, where the nonwovenfabric 150 is set.

The nonwoven fabric 150, before being set, can be cooled, for example byone or more of the above described cooled belt 8 and suctioning roller 6b.

As mentioned above, there can be a number of variants, for example in anembodiment there is no pre-heating device 4 a.

For example, in the absence of the pre-heating device 4 a, the crimpingcan be activated inside the heating device 4 b.

It has to be further noticed that a drum oven has been described as aheating device and a device with surface(s) parallel to thesubstantially straight forward direction D of the nonwoven fabric hasbeen described as a pre-heating device, respectively.

However, by varying the temperature of the flow of gases G1 or G2, it isnot excluded to use the parallel surface device as a heating device orto use the drum oven as a pre-heating device 4 a.

For example, in a possible variation, two parallel surface devicessimilar to the device 4 a shown in the figures can be used. Inparticular, the first device would operate analogously to thepre-heating device 4 a of FIGS. 1 and 2 whereas the second device,placed downstream of the first one, would generate a gas flow at atemperature between 90 and 190° C., so that to operate as a heatingdevice.

In a further exemplary variation, two drum ovens placed in series areused, i.e. as the pre-heating and heating devices.

1. An apparatus for producing a nonwoven fabric, comprising a spinneretfor extruding a plurality of filaments, and means for collecting thefilaments and forming a nonwoven fabric, at least one thermal treatmentdevice, at least one bonding device, wherein said at least one thermaltreatment device comprises at least one heating device configured todirect gas against said nonwoven fabric at a temperature between 80 and190° C.
 2. The apparatus according to claim 1, comprising a pre-heatingdevice configured to direct the gas (G1) against said nonwoven fabric ata temperature between 70 and 185° C.
 3. The apparatus according to claim1, further comprising a device for entangling said filaments to eachother is arranged upstream of said heating device and also saidpre-heating device, the entangling device including a couple of rollers,a needle loom or an ultrasound device.
 4. The apparatus according toclaim 2, further comprising a device for entangling said filaments toeach other is arranged upstream of said heating device and also saidpre-heating device, the entangling device including a couple of rollers,a needle loom or an ultrasound device.
 5. The apparatus according toclaim 1, further comprising cooling means comprising at least one among:a cooling device configured to direct a flow of gas against saidnonwoven fabric at a temperature between 30 and 140° C.; a suctioningroller; a cooled conveyor belt; and a suctioning roller.